We really can't say since there's no way to know how the original speakers pronounced things. We can somewhat confidently restore what Akkadian sounded like due to comparative semetic studies and their syllabic spelling in writing. However, Sumerian is a language isolate with no known related languages for comparison, their spelling was mostly logographic (think chinese, a single symbol representing an idea), and the only way we know the associated sounds is through Akkadian who didn't have the same sounds to be able to accurately represent how Sumerian was pronounced. For example it's believed that Sumerian had several o sounds that Akkadian is simply unable to render, and instead get represented as the same u sounds despite the variety that originally existed. You'll usually hear it pronounced with a soft g today but that has nothing to do with how it was originally pronounced